Suspended sediment flux at the Rhone River mouth (France) based on ADCP measurements during flood events

Suspended sediment distribution and fluxes were estimated within the dominant channel at the mouth of the Rhone River for two annual flood events. The estimates were based on ADCP acoustic backscatter intensity and using calibration and post-processing methods to account for the grain-size distribution (GSDs). The fluxes were very similar to those obtained from suspended sediment measurements based on surface sampling at an automated station located 35 km upstream. Suspended sediment concentrations (SSC) and GSDs showed little variation along the channel cross-section, except for a graduate suspension that appeared at the maximum of discharge, corresponding to velocities lower than 1 m s−1 near the bottom. However, without post processing to account for the GSD, an under-estimation of 10% was observed during the two flood periods. The two flood events (12 November 2012 and 29 November 2012), separated by only 2 weeks, had clear differences in suspended sediment fluxes (SSF) and SSC during the peak of the river discharge, with twice more flux during the first, respectively, 925,226 and 430,879 tons of SSF.